1. Field of the Invention
The present invention relates to fluids that are used with electrical equipment and transmission components, and in particular, to fluids used for electrical insulation and/or heat dissipation in electrical components, such as, for example, electrical transformers and electrical transmission lines.
2. Problems in the Art
The components that are used to generate and transfer electrical energy to end users, such as homeowners or businesses, are well known in the art. Electrical power producers generally generate electrical power at very high initial voltages. Handling of such high voltages requires substantial electrical insulation. It requires control of heat that is generated from the transmission of the electrical energy and maintenance of its dielectric properties.
It has been found that certain fluids have high insulating and heat dissipation properties. These fluids are used with such electrical components as transformers and fluid-filled transmission lines. One particular problem is that over time and with substantial exposure to high-voltage electricity the beneficial characteristics of such fluids, such as insulating and/or heat dissipation properties, degrade.
Conventionally, petroleum-based fluids are used for these types of applications. It must be appreciated that such fluids have certain properties that allow them to function satisfactorily. They must be electrically-insulating and dissipate heat. They must resist break-down. Synthetic fluids are also in use. However, currently used fluids have several deficiencies or concerns.
Most of the current fluids are minimally biodegradable. They pose safety or contamination concerns as they can be toxic to humans and animals. Many electrical components holding such fluids are situated near water or waterways. Leakage or spills can cause serious damage to water and marine life. Leaks or spills on land can threaten groundwater and contaminate soil.
Petroleum-based products are non-renewable. The amount of fluid of this type in use is significant. For example, one 15 MVA transformer (approximately serves 2000 customers, both residential and commercial) requires on the order of 3600 gallons of electrically-insulating fluid. One mile of fluid-filled transmission cable (6 inch diameter) requires about 7000 gallons. About 4.5 billion gallons of transformer oil are currently in use in the U.S. There are approximately 20,000 miles of high-pressure fluid-filled transmission cables (one type of the same) in the United States, most in larger cities and, therefore, most are near water or waterways.
As can be appreciated, significant amounts of resources, both time and money, are spent by electrical power companies in designing and implementing plans and systems to deter leaks or spills and to monitor transformers and transmission cables of these types for leaks or spills. It is estimated such costs are in the millions of dollars in the United States. Additionally, substantial resources are expended in reporting leaks or spills, even minor, because of environmental rules and regulations with regard to at least petroleum-based fluids. Of course, the effect of leaks or spills themselves can be very costly, as can remediation of the same.
Therefore, there have been attempts to look to new sources for such fluids, including vegetable oils. Such attempts would address both the environmental concerns as well as the issue of renewability of source as well as the potential for recycling into greases, for example, after use.
A similar problem exists with respect to petroleum- or synthetic-based lubricants. The idea of substituting vegetable oils for petroleum-based industrial lubricants is not new. Furthermore, finite supply of petroleum-based products, oil importation concerns, and concerns over environmental effects from spills/disposal of petroleum-based lubricants has fueled interest in the use of vegetable oils as viable substitutes.
Efforts to use vegetable oils as a substitute have focused upon less stringent uses such as hydraulic fluids, transmission fluids, and greases and not on the more severe automotive-type (engine) lubricants or transformer cooling oils. The vast majority of these endeavors have utilized vegetable oils high in natural oleic acid levels such as safflower oil, canola and rapeseed oils. The reason for the focused research upon these high oleic acid level vegetable oils is the tendency of natural vegetable oils to destabilize in use absent the presence of a high level of oleic acid. Other vegetable oils, such as soybean and corn oils, have a relatively low level of oleic acid and have been uniformly rejected in practical application because of the tendency of these oils to solidify while in use within the environment of high temperatures.
There are several fundamental properties transformer oils, for example, require, most of which are contrary to the natural properties of vegetable oils. These properties are oxidation stability, dielectric constant, pour point, sludge formation, and formation of acids. Of the vegetable oils, such as rapeseed, canola, and castor, commonly considered for industrial lubricants, soybean and corn oils are the more unstable (oxidatively) because of their unsaturated nature.
The primary purpose of the types of fluid needed for electrical transformers and fluid-filled transmission lines, hereinafter referred to as electrically-insulating fluid, is to maintain cooling properties and fluid characteristics while in use within the system so as to maintain appropriate temperature, as well as dielectric strength, on demand. The heat of the transformer unit, for example, can increase to high levels for extended periods of time which the fluid must be able to tolerate without losing its properties. Additionally, the operation of transformers and the process of heat dissipation at varied ambient temperatures subjects the fluid to constant stresses.
Some vegetable oil-based electrically-insulating fluids have found commercial success. These vegetable oil-based fluids have often been of the more naturally stable seed oils. Specifically, oils naturally high in oleic acid content or low in linolenic content, and in some cases low erucic acid, have been used. Variations in temperature, in particular high temperature environments, are known to impact the ability of a vegetable oil-based fluid to remain in the liquid state. As a result, this limited number of vegetable oils have been found to function with relative success.
Use of vegetable oil-based electrically-insulating fluids in the outdoors environment presents a much harsher challenge. To date, the success of such fluids has been very limited. Rapeseed and canola oil-based fluids have been commercially offered, but questions remain as to the functionality. These questions include sufficiency of electrical insulating properties and oxidation problems. Also, since crops such as rapeseed and canola are grown mainly outside the United States, it is expensive to import and produce which in turn increases the expense of making oils from them.
Because the above questions regarding rapeseed and canola oil exist, the same questions exist with respect to other less thermally stable oils, such as soybean and corn.
Soybean and corn oils, because of their unsaturated natures, lack desired oxidative stability for many industrial applications where continuous long-term heating takes place. In use, transformer and transmission line cooling oil must successfully operate not only to cool the components of the transformer and transmission line but also to not break down thereby changing its dielectric constant. The key characteristics required for such fluid use are:
1. High oxidation stability:
a. long life and protection;
b. no oxidation materials; and
c. no changes in chemical properties.
2. Viscosity Characteristics:
a. low pour point for cold temperature service, particularly in cold temperature regions; and
b. high Viscosity Index for best viscosity under various operating temperatures.
3. Corrosion Inhibition Properties:
a. inhibits contaminants in the fluid;
b. inhibits water;
c. inhibits oxidation by-products; and
d. inhibits changes in the fatty acids (in the case of vegetable oils).
4. Seal, Polymer, Resin Compatibility:
a. with old and new seal materials; and
b. with resin and other insulating materials.
Another demand placed upon electrically-insulating fluid is the requirement that it maintain a certain degree of stability in terms of insulating properties despite some of the physical and chemical changes that take place during extended use.
Therefore, it is a primary object of the present invention to present a composition and method which improve over and/or solves the problems and deficiencies in the art. Further objects of the invention include the provision of a vegetable oil-based composition and method which:
a. can be substituted for existing electrically-insulating fluids used in such electrical components as transformers and fluid-filled transmission lines, but is more environmentally-friendly and less toxic;
b. is more biodegradable than petroleum-based or some synthetic-based fluids;
c. has a renewable source;
d. meets the specifications and requirements typically recognized by the industry for such fluids and/or performs generally equivalently to existing fluids;
e. is relatively long-lasting and durable over a variety of operational and environmental conditions; and
f. is economical to make, use, and maintain.
These and other objects, features, and advantages of the resent invention will become more apparent with reference to the ccompanying specification and claims.
The present invention relates to a vegetable oil-based electrically-insulating fluid for use in electrical components that need such a fluid, such as for example, electrical transformers and fluid-filled electrical transmission cables or lines. A base oil made from vegetable oil, especially soybean and/or corn oil, is chemically modified by at least partial hydrogenation. To achieve this result, the base oil is optimized, through the process of hydrogenation, to produce maximum possible stability of the vegetable oil. This process is necessary for transformer equipment and transmission line applications. An antioxidant may be added to the base oil.
The vegetable-based oil of the present invention can be further processed with the additional step of winterization to remove crystallized fats and improve the pour point of the base oil without the necessity of heating the oil. An additive package for the present invention can be included which contains materials specifically designed for improving the properties of vegetable oil for this application.
The combination of the processed vegetable oil and additives produces an electrically-insulating fluid that withstands the rigors of field use involving a wide range of temperatures.
According to the invention, an electrical component containing the vegetable-based oil described above is set forth. The vegetable-based oil, contrary to existing petroleum-based or synthetic oils, is biodegradable and, therefore, safer to the environment and to living things. It also is based on a natural, renewable resource.